Long-Term Reconstitution of Transduced Rhesus CD34+ Cells Mobilized by G-CSF and Plerixafor.

Granulocyte colony-stimulating factor (G-CSF) in combination with plerixafor (AMD3100) produces significant mobilization of peripheral blood stem cells in the rhesus macaque model. The CD34+ cell population mobilized possesses a unique gene expression profile, suggesting a different proportion of progenitor/stem cells. To evaluate whether these CD34+ cells can stably reconstitute blood cells, we performed hematopoietic stem cell transplantation using G-CSF and plerixafor-mobilized rhesus CD34+ cells that were transduced with chimeric HIV1-based lentiviral vector including the SIV-capsid (χHIV vector). In our experiments, G-CSF and plerixafor mobilization (N=3) yielded a 2-fold higher CD34+ cell number, compared to that observed for G-CSF and stem cell factor (SCF) combination (N=5) (8.6 ± 1.8 × 10⁷ vs. 3.6 ± 0.5 × 10⁷, p<0.01). Transduction rates with χHIV vector, however, were 4-fold lower in G-CSF and plerixafor-mobilized CD34+ cells, compared to G-CSF and SCF (13 ± 4% vs. 57 ± 5%, p<0.01). CD123+ (IL3 receptor) rates were higher in CD34+ cells mobilized by G-CSF and plerixafor (16.4%) or plerixafor alone (21.3%), when compared to G-CSF alone (2.6%). To determine their repopulating ability, G-CSF and plerixafor-mobilized CD34+ cells were transduced with EGFP-expressing χHIV vector at MOI 50 and transplanted into lethally-irradiated rhesus macaques (N=3). Blood counts and transgene expression levels were followed for more than one year. Animals transplanted with G-CSF and plerixafor-mobilized cells showed engraftment of all lineages and earlier recovery of lymphocytes, compared to animals who received G-CSF and SCF-mobilized grafts (1200 ± 300/μl vs. 3300 ± 900/μl on day 30, p<0.05). One month after transplantation, there was a transient development of a skin rash, cold agglutinin reaction, and IgG and IgM type plasma paraproteins in one of the three animals transplanted with G-CSF and plerixafor cells. This animal had the most rapid lymphocyte recovery. These data suggested that G-CSF and plerixafor-mobilized CD34+ cells contained an increased amount of early lymphoid progenitor cells, compared to those arising from the G-CSF and SCF mobilization. One year after transplantation, transgene expression levels were 2–5% in the first animal, 2–5% in the second animal, and 5–10% in the third animal in all lineage cells. These data indicated G-CSF and plerixafor-mobilized CD34+ cells could stably reconstitute peripheral blood in the rhesus macaque. Next, we evaluated the correlation of transgene expression levels between in vitro bulk CD34+ cells and lymphocytes at one month, three months, and six months post-transplantation. At one and three months after transplantation, data from G-CSF and plerixafor mobilization showed higher ratio of %EGFP in lymphocytes to that of in vitro CD34+ cells when compared to that of G-CSF and SCF mobilization. At six months after transplantation the ratios were similar. These results again suggest that G-CSF and plerixafor-mobilized CD34+ cells might include a larger proportion of early lymphoid progenitor cells when compared to G-CSF and SCF mobilization. In summary, G-CSF and plerixafor mobilization increased CD34+ cell numbers. G-CSF and plerixafor-mobilized CD34+ cells contained an increased number of lymphoid progenitor cells and a hematopoietic stem cell population that was capable of reconstituting blood cells as demonstrated by earlier lymphoid recovery and stable multilineage transgene expression in vivo, respectively. Our findings should impact the development of new clinical mobilization protocols.

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No relevant conflicts of interest to declare.